When you eyes don't appear to be focused on anything, but rather staring into oblivion. Can be further emphasized if the person has been staring in the same direction long enough that moisture has built up on the eye, causing a slightly more glassy effect.

I was telling him about the new TPS reports this morning, but I feel like he wasn't even listening to me. He had glazed eyes and he didn't appear to be focused on my interesting dialog on TPS reports.